1. Field of the Invention
The present invention relates to a detecting circuit, more particularly to a detecting circuit for measuring an output of, for example, a prism-shaped vibratory gyroscope used a bending vibration.
2. Description of the Prior Art
FIG. 14 is a block diagram showing an example of a conventional detecting circuit which is a background of the present invention. The detecting circuit 1 is used for detecting an output of, for example, a triangular prismshaped vibratory gyroscope 2. Between two piezoelectric elements 3 and the other piezoelectric element 4 of the vibratory gyroscope 2 , an oscillation circuit 5 is connected. In this case, the oscillation circuit 5 is connected respectively to the two piezoelectric elements 3 of the vibratory gyroscope 2 via resistors 6. Outputs of the piezoelectric elements 3 are applied to a differential amplifier circuit 7. An output of the differential amplifier circuit 7 is converted into a DC output by a smoothing circuit 9 via a synchronous detection circuit 8.
By the oscillation circuit 5, the vibratory gyroscope 2 bends and vibrates in the direction perpendicular to the surface of the piezoelectric element 4. In this time, output signals from the two piezoelectric elements 3 are the same signal, an output from the differential amplifier circuit 7 becomes zero. When the vibratory gyroscope 2 is rotated about its axis, a Coriolis force is generated in the direction perpendicular to the vibrating direction of the vibratory gyroscope 2. The vibrating direction of the vibratory gyroscope 2 is shifted from the vibrating direction at non-rotation. A difference of outputs is generated between the two piezoelectric elements 3, an output is obtained from the differential amplifier circuit 7. The output becomes the value corresponding to the magnitude of the rotational angular velocity. The output is smoothed by the smoothing circuit 9 via the synchronous detection circuit 8, and an output of the smoothing circuit 9 is measured, thereby the rotational angular velocity applied to the vibratory gyroscope 2 can be measured.
However, the electrostatic capacities of the piezoelectric elements change by an atmospheric temperature, a change with time and so on, a drift signal is generated from the differential amplifier circuit even during non-rotation. The drift signal causes an error in measurement, it is impossible to measure an accurate rotational angular velocity.